1. Field of the Invention
The invention relates to multimedia methods, devices and bit streams in particular those applying a high-level content description, by for instance using XML-like documents like in the so-called bit stream syntax description languages like BSDL or variants or derivatives thereof. The present invention particularly relates to image coding techniques wherein a block-based arrangement of the image is considered. The image coding technique generates a packetized bit stream. The present invention also relates to a description of an encoded bit stream, a method for transforming such a description so as to generate an adapted description and a method of generating an adapted encoded bit stream from an original encoded bit stream. The invention also relates to an electronic device designed for implementing such a method of transforming a description. The invention also relates to a transmission system comprising a transmitter and a receiver, the transmitter having means for implementing such a method generating an adapted encoded bit stream from an original encoded bit stream, and means for transmitting the adapted encoded bit stream to the receiver. The invention can be applied to images/video transmission.
2. Description of the Related Technology
Bit stream Syntax Description Languages (BSDL or similar) was introduced in: [“Bit stream Syntax Definition Language: an input to MPEG-21 Content Representation”, ISO/IEC JTC1/SC29/WG11 MPEG01/IM7053, Singapore, March 2001] and [Sylvain Devillers, Myriam Caprioglio, “Bit stream Syntax Definition Language (BSDL)”, ISO/IEC JTC1/SC29/WG11 MPEG01/M7433, Sydney, July 2001.] as an efficient and platform independent way to describe and adapt multimedia content. This XML-schema based languages allow describing the content of a multimedia file in a comprehensible and structured way that can be modified using XSLT and brought back to a binary form. The possibility of transforming multimedia files is very attractive from the point of view of content scalability.
Today, whereas streaming video is common practice, the streaming of 3D content remains rare, or even nonexistent. When decoding and rendering 3D content, the workload on the consumer's platform heavily varies over several orders of magnitude with the viewing conditions. As mostly only a part of the textured 3D objects is visible at any given time, streaming and/or decoding only the visible regions of the texture will reduce instantaneous bandwidth and/or platform workload. When the viewing conditions change, the newly visible parts can be streamed and/or decoded as they gradually become visible. Consequently, the required network bandwidth as well as the required workload for decoding and rendering textured 3D content are spread over time while minimizing the perceived quality loss. This process is known as view-dependent texture decoding [D. Cohen-Or, Y. Mann, S. Fleishman, “Deep Compression for Streaming Texture Intensive Animations,” Proceedings of the SIGGRAPH 1999 annual conference on Computer graphics, pp. 261-267, 1999.].
Within the MPEG-4 multimedia compression standard [“The MPEG-4 Audio-Visual Compression Standard, Text of ISO/IEC 14496-5/FPDAM1,” ISO/IEC JTC1/SC29/WG11/MPEG99/N3309, Noordwijkerhout, March 2000.], tools are available for coding 3D content. In particular, MPEG-4 provides a scalable, wavelet based, compression tool for textures, called Visual Texture Coding (VTC) [I. Sodagar, H. J. Lee, P. Hatrack, Y. Q. Zhang, “Scalable Wavelet Coding for Synthetic/Natural Hybrid Images,” IEEE Transactions on Circuits and Systems for Video Technology, Vol. 9, No. 2, pp. 244-254, March, 1999.].
VTC allows the generation of a packetized bit stream with a high flexibility for defining the packet boundaries. Each packet consists of a number of basic units, called texture units (TU). A particular case in VTC is the multiple quantization, tree-depth mode (MQ-TD).
The maximum granularity provided in the MQ-TD mode is given by the number of wavelet transform levels. The number of pixels involved in the transformation increases as the size of the block is 2n—levels×2n—levels. As error resilience introduces some overhead, limiting the granularity can reduce the size of the compressed image. Several transform spatial blocks can be grouped in a single packet instead of introducing an error resilience marker after each block. This can be useful when only coarse granularity is required.
Known multi-media formats tend to hide information, which can be vital for the multimedia content adaptation process, but is embedded in the bit stream.
A method for transforming a description of a bit stream is described in the international patent application WO 02/063494 filed by Koninklijke Philips Electronics N.V. The method described in this document includes:                using an original description of a bit stream written in a markup language, and a set of predefined transformations,        applying one of the predefined transformations to the original description so as to generate an adapted description,        generating an adapted bit stream from the adapted description.        
In the method described in this document, the original description has to be detailed enough to allow recovering the coding information that is required for performing the transformations. Such a detailed description can be considerably verbose, and there is a need for descriptions that are easier to adapt. It would also be useful to have simpler and shorter descriptions.